nri: add experimental NRI plugin.

Add a common NRI 'service' plugin. It takes care of relaying
requests and respones to and from NRI (external NRI plugins)
and the high-level containerd namespace-independent logic of
applying NRI container adjustments and updates to actual CRI
and other containers.

The namespace-dependent details of the necessary container
manipulation operations are to be implemented by namespace-
specific adaptations. This NRI plugin defines the API which
such adaptations need to implement.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

vendor/github.com/opencontainers/runtime-tools/generate/seccomp/consts.go

@@ -4,9 +4,4 @@ const (
 	seccompOverwrite = "overwrite"
 	seccompAppend    = "append"
 	nothing          = "nothing"
-	kill             = "kill"
-	trap             = "trap"
-	trace            = "trace"
-	allow            = "allow"
-	errno            = "errno"
 )